Soldier's Heart is based on a true story about a fifteen-year-old boy in Minnesota named Charley Goddard who lies about his age to join the First Volunteers of Minnesota to fight in the Civil War. Some of the events and time sequences are not completely factual, but the essential elements of the book's story are true.

Charley Goddard is a fifteen-year-old boy growing up in the farming community of Winona, Minnesota, in 1861, just prior to what will become the Civil War. The whole area is talking about what they think will be a "shooting war." The atmosphere at the town meetings discussing the possibility is festive, with flags and drums and patriotic speeches.

As a volunteer army is beginning to form, Charley decides he wants to be part of it. Everyone assumes that it will be an easy, victorious battle, most likely over in a month...